A vessel for containing convenience food such as instant noodles or instant YAKISOBA (snack noodles) which can be cooked by pouring hot water into the vessel, or for containing food which is desired to be eaten while it is hot may be made of a formed product of a foamed synthetic resin. This is preferable because the heat insulating property inherent in the foamed synthetic resin causes the temperature of the contents to be hardly transferred to a hand holding the vessel, and the contents to be hardly cooled.
FIG. 14 shows a part of a heat insulated vessel A of the prior art which is made of a foamed synthetic resin. In the vessel, an annular flange 4 is radially outwardly projected from and continuous with an opening edge 11 of a bottomed cylindrical portion 1 in which a barrel wall portion 3 extends from a bottom wall portion 2.
Conventionally, such a heat insulated vessel A can be produced by the bead foam forming method. However, a vessel produced by the bead foam forming method has problems in that the surface roughness is large and that the production cost is high.
By contrast, a heat insulated vessel is sometimes produced from a foamed synthetic resin sheet by the vacuum forming method or the air-pressure forming method. In these methods, vessels are simultaneously formed at plural positions of a foamed synthetic resin sheet by the method described above, and thereafter the formed vessels are punched out from the foamed synthetic resin sheet so that the vessels are individually taken out. In the heat insulated vessel A which is taken out from the foamed synthetic resin sheet by punching, however, the outward end face 41 of the annular flange 4 corresponds to the cut face of a large surface roughness. Therefore, such a vessel has problems in that the end face 41 is so conspicuous that the external appearance of the heat insulated vessel A is bad-looking, and that, when the contents are eaten or drunk by putting the lips to the annular flange 4, the flange hardly hits against the lips, so that a physical disorder may be produced on the lips and, in an extreme case, the lips are cut or injured, thereby lowering the value of this product.
As discussed above, the prior art heat insulated vessel A made of a foamed synthetic resin, particularly the annular flange 4 shown in FIG. 14 is susceptible to improvement. Conventionally, the heat insulated vessel A is produced with a view to economical efficiency, size, heat insulating property, and rigidity. From this point of view, also the annular flange 4 is made as an annular flange which is very thick or has a thickness equal to that of the barrel wall portion 3 of the heat insulated vessel A. As a result, the thick annular flange 4 cannot be subjected to a forming process in which a designed shape is made, before the forming of the heat insulated vessel A and also after the forming. In the art, therefore, it seems that the annular flange 4 cannot be improved.